Dynamic Mechanical Thermal Analysis Research Articles

The Effect of Molecular Weight on the (Re)-Processability and Material Properties of Bio-Based, Thermoreversibly Cross-Linked Polyesters

A (partially) bio-based short-chain polyester is prepared through interfacial polycondensation of furan-functionalized diphenolic acid with terephthalic chloride. The furan groups along the backbone of the obtained polyester are able to form a covalent network (PE-fur/Bism) with various ratios of 1,1′-(methylenedi-4,1-phenylene)bismaleimide via the thermoreversible Diels–Alder (DA) reaction. Several techniques have been employed to characterize the polyester network, including 1H-NMR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The polyester base polymer displays a glass transition temperature of 115 °C, whereas the temperatures at which the retro-Diels–Alder (rDA) reaction takes place lie above 130 °C for the various polyester/bismaleimide networks. Excellent thermoreversibility and recyclability of the polyester resin have been shown through DSC and DMTA measurements.

Cationic photopolymerization of cyclic esters at elevated temperatures and their application in hot lithography

AbstractThe 3D printing of polyesters is most commonly performed using polylactide filaments for material extrusion (formerly known as fused‐deposition modelling) or by introducing methacrylate end‐groups to polyesters, which can be polymerized by a radical mechanism. However, cyclic esters can also be polymerized via cationic ring‐opening photopolymerization, which opens up the possibility of using high‐resolution stereolithography as the method of choice to form polyester networks in situ during the printing process. Hereby, we present the first approach to 3D print polyesters starting directly from ε‐caprolactone via stereolithography at elevated temperatures, by introducing low amounts of crosslinks into the material to provide stability to the structure but maintain its degradable character and especially semicrystallinity. Photorheology tests showed that high temperatures and the introduction of crosslinkers led to increased reactivity and fast gelation. By performing tensile tests, dynamic mechanical thermal analysis and simultaneous thermal analysis the material properties were evaluated depending on the amount and type of crosslinker. It was shown that decreasing the amount of crosslinker significantly increased the crystallinity and influenced the mechanical properties as well as shape memory properties. Finally, successful 3D printing of a polyester was performed using 10 mol% of a crosslinker with oxetane moieties and 90 mol% ε‐caprolactone at 120 °C. © 2022 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Morphological and Viscoelastic Properties of the Cicada Tymbal

This paper focusses on the morphological and viscoelastic properties of the cicada tymbal from the species Dundubia rufivena. Morphological details were determined by scanning electron and fluorescence microscopy, while the viscoelastic properties were determined by dynamic mechanical thermal analysis, and further supported by differential scanning calorimetry. We find that water evaporation from the tymbal begins at 71.1 °C and the glass transition for the tymbal, which is a chitin–resilin composite, is on average 150 °C, though there is considerable heterogeneity in the material of the tymbal, as indicated by the half height peak width of the tymbal (35.3 °C) and the shoulder peak indicative of a second phase and hence glass transition at on average, 168 °C. This second phase is assumed to reflect the effects of large-scale molecular pinning and restructuring at resilin–chitin interfaces (possibly via specific binding domains). In addition, we elucidate that the predominantly resilin regions of the tymbal of Dundubia rufivena is reinforced by a polygonal mesh of chitin, a morphological feature that has not been described in any previous research on the cicada tymbal. We provide evidence for nonlinear elasticity in the tymbal by comparing the storage modulus of the tymbal at different frequencies and loading amplitudes.

Synthesis and characterization of poly(hexamethylene 2,6-naphthalate)-block-poly(tetrahydrofuran) copolymers with shape memory effect

Shape memory polymers (SMPs) are able to return to their previous shape after deformation under certain conditions. Several block copolymers can exhibit shape memory behavior. The blocks in copolymers are usually immiscible, which leads to phase separation into rigid and flexible segments. For that reason, these materials combine the mechanical properties of elastomers with the processing properties of thermoplastic. Thus, a poly(hexamethylene 2,6-naphthalate) (PHN) and a series of poly(hexamethylene 2,6-naphthalate)-block-poly(tetrahydrofuran) (PHN-b-N-pTHF) copolymers were synthesized via melt polycondensation. The content of the N-pTHF flexible segment varied from 15 to 50 wt.%. The materials were characterized with the use of Fourier transformed infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), X-ray diffraction (XRD) analysis, the tensile tests (static and cyclic), and the cyclic thermo-mechanical analysis. The PHN-b-N-pTHF 50/50 was proved to be a promising thermoplastic shape memory polymer (SMP).

Moisture sorption characteristics and dynamic mechanical thermal analysis of dried petiole and rhizome of red water lily (Nymphaea x rubra)

Moisture sorption characteristics and dynamic mechanical thermal analysis of dried petiole and rhizome of red water lily (Nymphaea x rubra)

Thermal Rheological Behavior of Composite Interlayer in Laminated Glass

Laminated glass is growing its application in structural entities. The thermoplastic polymeric interlayer plays an important role in transferring force and achieving the composite action in laminated glass, which reveals evident temperature-dependent behavior. In this study, a novel composite interlayer (SGE®) was devised to improve the resistance of laminated glass against environmental actions and to enhance the post-fracture performance. It is comprised of modified ethylene-vinyl-acetate (PVE®) and polycarbonate (PC). Through dynamic mechanical thermal analysis, the temperature-dependent characteristics of SGE, PVE, and PC materials were investigated in detail. The results show that the thermal rheological behavior of SGE is similar to that of PVE. The temperature ranges of glass transition and crystal melting of SGE material are -35°C ~ -25°C and 45°C ~ 75°C, respectively. The corresponding ranges are -35°C ~ -15°C and 35°C ~ 65°C for PVE material. And temperature ranges of the main transition are influenced by imposed frequency. Besides, the relationship between time and temperature for PVE, PC, and SGE material is extensively complicated and the complexity depends on the investigated mechanical property, temperature range, and time range. And the simple thermal rheological behavior emerges in the storage modulus of polymers, but loss modulus and loss factor conform to the complex thermal rheological behavior at the temperature range of -50°C ~ 120°C under the frequency range of 0.1 Hz ~ 10 Hz.

Influence of Carbon Micro- and Nano-Fillers on the Viscoelastic Properties of Polyethylene Terephthalate.

In this research study, three carbon fillers of varying dimensionality in the form of graphite (3D), graphite nano-platelets (2D), and multiwall carbon nanotubes (1D) were incorporated into a matrix of poly (ethylene terephthalate), forming carbon-reinforced polymer composites. Melt compounding was followed by compression moulding and then a quenching process for some of the samples to inhibit crystallization. The samples were analysed using dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM), considering the dimensionality and loading of the carbon fillers. The dynamic mechanical analysis revealed a similar decline of storage moduli for all composites during the glassy to rubbery transition. However, storage moduli values at room temperature increased with higher loading of nano-fillers but only to a certain level; followed by a reduction attributed to the formation of agglomerates of nanotubes and/or rolled up of nano-platelets, as observed by SEM. Much greater reinforcement was observed for the carbon nanotubes compared to the graphite and or the graphite nano-platelets. The quenched PET samples showed significant changes in their dynamic mechanical properties due to both filler addition and to cold crystallization during the DMTA heating cycle. The magnitude of changes due to filler dimensionality was found to follow the order: 1D > 2D > 3D, this carbon filler with lower dimensionality have a more significant effect on the viscoelastic properties of polymer composite materials.

Synthesis, characterization, and properties of a new polyurethane elastomer based on tragacanth gum polysaccharide

This study prepared a type of bio-based elastomeric polyurethane from tragacanth gum (TG). TG is a natural polysaccharide with many hydroxyl groups that can be used as a chain extender and a crosslinker to react with the isocyanate groups in polyurethane prepolymer to form a highly branched and crosslinked polyurethane with high molecular weight and good mechanical properties. The chemical structure of the prepolymer and the thermal and mechanical properties of the prepared polyurethane were studied by Fourier transform infrared, nuclear magnetic resonance, scanning electron microscopy, thermal gravimetric analysis, dynamic mechanical thermal analysis, and tensile strength tester. The properties of the polyurethane-based on TG (TG-PU) were compared with the properties of the PU based on only polyethylene glycol. The TG-PU sample with 0.5 g TG showed a tensile strength of 288% and the glass transition temperature (Tg) of 33% higher than the tensile strength and Tg of PU without TG. We expect these findings to widen the range of preparation and applications of bio-based polyurethane materials.

Effect of Nanoclay Filler on Fatigue Life of Natural Rubber/Styrene-Butadiene Blend

In this paper, the fatigue life of natural rubber (NR)/styrene-butadiene rubber (SBR) compound is evaluated experimentally. The parameters investigated are the NR, SBR, and nanoclay loading in the composition, strain amplitude, and the frequency of the fatigue test. Fracture surfaces of NR/SBR/nanoclay compound are investigated using scanning electron microscopy (SEM). The results show that by increasing NR and the nanoclay loading in the rubber composition, the fatigue life of the rubber increases. For the nanoclay, a threshold value exists beyond which the fatigue life of the rubber compound decreases. It is also observed that by increasing the test frequency, the fatigue life of the rubber compound decreased. Tensile, hardness, and dynamic mechanical thermal analysis (DMTA) tests were also performed to evaluate the mechanical and thermal properties of the compound. SEM results show that by increasing the strain amplitude, the test specimens fail softly, and the addition of nanoparticles roughens the fracture surface and increases the fatigue life.

Transparent Polymer Blends of Poly(methyl methacrylate) and Poly(propylene glycol).

Polymer blends, obtained by polymerization of methyl methacrylate in the presence of poly(propylene glycol), are investigated. Poly(propylene glycol) acts as a plasticizer, significantly lowering poly(methyl methacrylate)’s glass transition temperature and decreasing its elasticity modulus and yield stress. The mixture of methyl methacrylate with poly(propylene glycol) is more stable than its mixture with currently used poly(ethylene glycol), which leads to more uniform distribution and higher possible content of the plasticizer. Unlike low molecular weight plasticizers, poly(propylene glycol) is less prone to migration and exudation during manufacturing process and in use, and has low toxicity. Dynamic mechanical thermal analysis, compression testing and X-ray diffraction were used to investigate how the properties of the material depend on the content and molecular weight of the poly(propylene glycol) in the polymer blend. It was shown that the dependence of the glass transition temperature of methyl methacrylate polymerized in the presence of poly(propylene glycol) on the molar fraction of propylene glycol units is linear, and poly(propylene glycol) with lower molecular weight affects properties of the material stronger than poly(propylene glycol) with higher molecular weight. Therefore, the addition of poly(propylene glycol) allows to control the properties of poly(methyl methacrylate) easily and within wide range.

Development of an Analytical Model to Predict Stress–Strain Curves of Short Fiber-Reinforced Polymers with Six Independent Parameters

Mechanical properties of fiber-reinforced polymers are sensitive to environmental influences due to the presence of the polymer matrix but inhomogeneous and anisotropic due to the presence of the fibers. Hence, structural analysis with mechanical properties as a function of loading, environment, design, and material condition produces more precise, reliable, and economic structures. In the present study, an analytical model is developed that can predict engineering values as well as non-linear stress–strain curves as a function of six independent parameters for short fiber-reinforced polymers manufactured by injection molding. These parameters are the strain, temperature, humidity, fiber content, fiber orientation, and thickness of the specimen. A three-point test matrix for each independent parameter is used to obtain experimental data. To insert the effect of in-homogenous and anisotropic distribution of fibers in the analytical model, microCT analysis is done. Similarly, dynamic mechanical thermal analysis (DMTA) is done to insert the viscoelastic effect of the material. The least mean square regression method is used to predict empirical formulas. The standard error of regression for the fitting of the model with experimental stress–strain curves is closely controlled below 2% of the stress range. This study provides user-specific material data for simulations with specific material, loading, and environmental conditions.

Mechanical properties and degradation of laser sintered structures of PLA microspheres obtained by dual beam laser sintering method

This paper discusses the influence of process parameters on the degradation and the mechanical properties of laser-sintered polylactide (PLA) microspheres obtained using the novel dual beam laser sintering method (DBLS). DBLS is a technique developed by our team that is a modification of standard polymer laser sintering (pLS), with the potential to reduce polymer degradation during the process. The PLA microspheres were produced using the standard emulsion-solvent evaporation method. The laser sintering process was carried out in a wide range of process parameters to obtain samples with various degrees of sintering. Next a number of tests were conducted to assess the physicochemical properties of these samples, including visualization techniques (SEM, digital microscopy and photography), gel permeation chromatogrphy (GPC), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA) and static compression tests. The work shows that for different sets of process parameters, it is possible to obtain a product with similar mechanical properties, but at the same time with a completely different degree of polymer degradation. Hence, the hypothesis that when assessing the sinter quality one should take into account not only the mechanical properties of the detail, but also the degree of polymer degradation, which is of great importance, for example, in biomedical applications. It has also been shown that the DBLS method has a potential to reduce the degree of degradation of the sintered polymers and the post-process material outside the sintering zone.

Influence of the Reaction Injection Moulding Process on the Thermomechanical Behaviour of Fast Curing Polyurethane

In this contribution, the influence of the reaction injection moulding process on the thermomechanical material behaviour of aliphatic hexamethylene diisocyanate (HDI) based fast curing polyurethane is demonstrated. Uniaxial tensile tests, temperature-frequency dependent dynamic mechanical thermal analysis (DMTA) and Differential Scanning Calorimetry (DSC) are used to show the differences in properties for ten different sets of process parameters. The mould and resin components temperature, the mass flow during the filling process and the residence time during the reaction process of the polyurethane are varied in several stages. Further experiments to determine the molar mass of the molecular chain between two crosslinking points of the polyurethane are used to explain the process influences on the thermomechanical properties. Thus, a direct correlation between manufacturing and material properties is shown. In addition, the mutual effect of the different parameters and their overall influence on the material behaviour is presented.

Surface Modification of Magnesium Oxysulfate Whisker Based on SiO2@silane Coupling Agent and SiO2@polydopamine Double-Layer Structure for Reinforcing HDPE.

In this study, we fabricated high-performance polyethylene composites by constructing SiO2@silane coupling agent (γ-methylacryloxypropyl trimethoxysilane) and SiO2@polydopamine (PDA) double-layer structures on a magnesium oxysulfate whisker surface. In addition to realizing strong mechanical properties, the flame-retardant properties of the composites were effectively improved. Further increase in the initial crystallization temperature of the modified composites indicated that the dispersion of whisker in the matrix was improved. The drag effect of the modified whisker on the HDPE molecular chain was characterized by dynamic mechanical thermal analysis (DMTA) and the morphology of the impact-fractured surface was characterized by scanning electron microscopy (SEM); both confirmed the improved compatibility between the whisker and the matrix. The tensile strength of HDPE/MOSw@SiO2@KH570 and HDPE/MOSw@SiO2@PDA composites were 22.6% and 41.5% higher than that of the HDPE/MOSw composites, respectively. The impact strengths of the HDPE/MOSw@SiO2@KH570 and HDPE/MOSw@SiO2@PDA composites were 129% and 102% higher than that of the HDPE/MOSw composites, respectively. A stable carbon-silicate layer constructed by a SiO2@KH570 and SiO2@PDA double-layer structure delayed the combustion process. As a result, the limiting oxygen index (LOI) of HDPE/MOSw@SiO2@KH570 and HDPE/MOSw@SiO2@PDA composites increased from 22.5 to 22.9 and 23.5, respectively.

Poly(amidoamine)-grafted Graphene Oxide/Epoxy Nanocomposite: Thermal/ Mechanical Characteristics and Viscoelastic Properties

As the most crucial choice in the heavy-duty protective coating industry, epoxy-based coatings suffer from insufficient toughness and impermeableness. So in this study, a reliable method that is, in turn, easy to be scaled up is designed and proposed. Through this method, a significantly toughened and mechanically improved epoxy nanocomposite film is suggested. This film is based on poly(amidoamine)-grafted (PAMAM) graphene oxide (GO). GO is synthesized and then modified through two consecutive steps; first, silane-grafted GO producing SiGO and second polyamidoamine (PAMAM)-grafted SiGO leading to HbpSiGO. FT-IR, TGA, and XRD results confirm a successful functionalization of the GO flakes. Dynamic mechanical thermal analysis (DMTA) results reveal that the nanocomposite film based on HbpSiGO possesses higher storage modulus (50 %), elevated glass transition temperature (18 %), and higher cross-linking density (237 %) compared to unfilled epoxy. According to tensile testing, HbpSiGO nanocomposite shows an increment in work of fracture (148%), elongation at break (52 %), and maximum stress (68 %) in comparison with neat epoxy.

Experimental and Theoretical Analysis of Mechanical Properties of Graphite/Polyethylene Terephthalate Nanocomposites.

In this work, graphite nanoplatelets (GNP) were incorporated into poly (ethylene terephthalate) (PET) matrix to prepare PET-GNP nanocomposites using a melt compounding followed by compression moulding and then quenching process. Both static and dynamic mechanical properties of these quenched materials were characterized as a function of GNP contents using dynamic mechanical thermal analysis (DMTA) and tensile machine, respectively. The results demonstrated that the addition of GNP improved the stiffness of PET significantly. Additionally, the maximum increase in the storage modulus of 72% at 6 wt.% GNP. The incorporation of GNP beyond 6 wt.% into PET decreases the storage moduli, but they remain higher than pure PET. The observed reduction could be due to agglomeration, resulting in poorer dispersion and distribution of higher levels of GNP into the PET matrix. In contrast to the results for moduli, tensile strength and elongations at break reduce with increasing the GNP content. For example, tensile strength reduced from ∼46 MPa (neat PET) to ∼39 MPa (−15%) for the nanocomposites containing 2 wt.% GNP. This reduction is accompanied by a decline in elongation at break from ∼6.3 (neat PET) to ∼3.4 (−46%) for the same nanocomposites. Such reductions are followed by a gradual decrease in upon further addition of GNP. These reductions indicate that increasing GNP loadings, results in brittleness in nanocomposites. In addition, it was found that quenched PET and composite samples were not fully crystallized after processing and therefore (cold) crystallized during the first heating cycle DMTA, as indicated by a rise in storage moduli above the glass transition temperature during the DMTA first heat. Furthermore, mathematical models based on non-linear theories are developed to capture the experimental data. For this, a set of mechanical stress-strain data is used for model parameters’ identification. Another set of data is used for the model validation that demonstrates good agreements with the experimental study.

Cross‐Linking of Biobased Monofunctional Furan Epoxy Monomer by Two Steps Process, UV Irradiation and Thermal Treatment

AbstractAmong the new generation of green polymers, furan monomers are occupying a strategic role to produce both innovative biobased thermoplastic and thermoset. Herein, furfuryl glycidyl ether (FGE) is used as monomer to design two steps cured coating. Linear polymer chains are first produced by means of cationic UV technique. The UV reactivity of FGE is assessed by real‐time Fourier Transform Infrared Spectroscopy (FTIR). Then, a thermal treatment is carried out to crosslink the UV‐irradiated linear chains. The formation of cross‐links is proven by means of different techniques. ATR‐FTIR shows the development of new chemical bonds by the appearance of new bands. Differential scanning calorimetry analysis confirms the cross‐link reaction by the presence of exothermic peaks and the dynamic mechanical thermal analysis reveals an increase of the Tg as direct consequence of cross‐links formation. Moreover, the %gel analysis confirms the formation of highly insoluble fraction after the cross‐linking.

Study on dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials based on DMA

Abstract Nonwater reacted polyurethane grouting materials are new materials developed to make up for the shortcomings of water-reactive materials in emergency rescue. However, its viscoelastic properties and constitutive model under dynamic loads have not been systematically studied. Based on dynamic thermal mechanical analysis (DMA), the dynamic viscoelastic indexes such as storage modulus, loss modulus, and loss factor of nonwater reacted polymer grouting material were obtained, and the frequency spectrum of polymer with different densities were analyzed. In addition, comparing and analyzing the classical viscoelastic constitutive models such as Maxewell model, Kelvin model, and Fractional model, the fourth-order generalized Maxwell model (GMM) was selected to construct the viscoelastic constitutive model of polyurethane grounding materials. Then, the parameters of the viscoelastic constitutive model of polyurethane grounding materials were obtained by using multi-objective shared parameter fitting method, and dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials was established. Furthermore, the viscoelastic constitutive model with different densities was verified by the DMA test. The results show that the dynamic viscoelastic constitutive model of nonwater reacted polyurethane grouting materials in the article can accurately and efficiently describe the dynamic viscoelastic properties of polyurethane grounding materials, which lays a foundation for the dynamic response analysis of polymer structures.

Development of PAMAM dendrimer-modified magnetic polyoxometalate: A novel platform to reinforce mechanical and thermal properties of diglycidyl ether of bisphenol A/isophorone diamine hardener epoxy

The present study explores the mechanical and thermal properties of DGEBA/IPD epoxy reinforced with dendrimer-functionalized magnetitepolyoxometalate nanoparticles. Magnetic iron oxide nanoparticles (MNP’s) were stabilized and functionalized by the poly (amido-amine) dendrimer via encapsulation within dendrimer; afterwards, H9 [α-P2V3W15O62] polyoxometalate (POM) was modified with dendrimer-functionalized magnetic iron oxide nanoparticles (DMNP’s). The polyoxometalate can be complexed with DMNP’s via protonation of dendrimer amino groups. In the next step, dendrimer-functionalized magnetitepolyoxometalate nanoparticles (DMNP’s-POM) were loaded into diglycidyl ether of bisphenol A (DGEBA) epoxy resin. The DMNP’s-POM nanoparticles can initiate polymerizations of epoxy resin with isophorone diamine hardener (IPD); on the other hand, the terminal amino groups of the dendrimer in the DMNP’s-POM nanoparticles allow them to be covalently linked to the polymer matrix alongside the main amine hardener. The resulting epoxy/magnetitepolyoxometalate nanocomposites (DMNP’s-POM@EN 5%) are thoroughly characterized by FT-IR, FE-SEM, and XRD analysis. Probing thermal behaviors of epoxy/magnetitepolyoxometalate nanocomposites by TGA reveals that the resulting composites are degraded thermally through a simple one-step process with an initial degradation close to 340°C, and show significant stability toward heat. Dynamic Mechanical Thermal Analysis indicates that no considerable agglomerate is formed during the synthesis process, and the incorporated nanoparticles somewhat limit the segmental motions of the epoxy macromolecular chains.

Rheological, flame retardancy, and thermomechanical properties of polymethyl methacrylate composites: Effects of flame retardant and toughener

AbstractIn this work, polymethyl methacrylate (PMMA) composites modified with diethylaluminum phosphonate (ADP) and epoxy resin (EP) as flame retardant and toughener, respectively, were prepared via solution method for improvement on both flame retardancy and toughening purposes. The effects of ADP and EP loadings on the viscoelastic, flame retardant and thermomechanical behaviors of the resultant composites were intensively investigated using rheometer, CONE calorimetry, oxygen index (LOI) and dynamic mechanical thermal analysis (DMTA), respectively. Heat flux complexity was obviously displayed when ADP and EP loadings increased. DMTA result showed that the increase of the modulus of the composites was primarily due to an interpenetrating polymer network (IPN) formed by the addition of EP, and the tensile properties were found to be greatly improved. In addition, our study also showed that at an ADP loading of 28% the maximum heat release rate (pHRR) of composites decreased by 63% as compared to neat PMMA with increase by 88% in LOI and V‐0 grade in UL‐94 test achieved. The composites prepared in this study bore excellent fire performance together with desired toughness, and the current work thus has practical significance for further expanding the application range of PMMA composites.